This invention relates to the art of forming glass articles from molten glass, and more particularly to a process of press forming a plurality of virtually identical soft parisons or blanks with a predetermined cavity press formed therein and extending downwardly below a blank supporting surface, which performed soft blank is subsequently blown into a final hollow glass article.
In the past it has been known to form parisons for press and blow operations by conventional means such as the Hartford I.S. machine, the Miller press and blow machine and the Lynch MB machine. The Hartford I.S. machine utilizes a plurality of blank molds, each with its own plunger, blowhead and neck ring. With the mold, plunger and neck ring in position, a charge is received in the mold and blown down so that the plunger forms the finish in the neck ring. After a counter blow the parison is completely formed and the blank mold opened with the glass parison held by the neck ring which is then rotated 180.degree. in a vertical plane to a position over a closing blow mold, wherein the neck ring is opened to release the parison into the blow mold and is then rotated back into position with the mold and plunger for a repeat cycle. From the time that the gob initially enters the blank mold until the time that the blank mold is opened, the molten glass may be in contact with the mold for in excess of 8 seconds, which materially reduces the temperature of the blank or parison thus forming a hard parison and requiring reheating of the blank surface from heat retained within the core of the blank in order to blow the parison into a finished article.
Both the Miller press and blow machine and the Lynch MB machine utilize rotating tables having a plurality of molds thereon for forming the blank or parison, wherein the tables are rotated with an intermittent or cyclic movement such that the molds stop at each station. Whereas the Miller press and blow machine uses one plunger for forming the blank and transfers the same by use of a neck ring, the Lynch MB machine utilizes individual plungers for each mold and transfers the parison from a blank mold table to a blow mold table by means of a swing transfer mechanism. Here again, however, the initial blank or parison is in contact with the blanking mold for an extended period of time in excess of 5 seconds for the Miller machine and greater than 8 seconds for the Lynch MB machine, again producing a hard blank which must have its exterior surfaces reheated from heat retained in the inside of the blank in order to accomplish the final blow. A more complete explanation of the operation of the Hartford I.S. machine, the Miller press and blow machine and the Lynch MB machine is set forth on pages 326-339 of Handbook of Glass Manufacture, Vol. 1 by Fay V. Tooley. However, from the foregoing it can be seen that the devices of the prior art include extended gob residence time in the blank mold resulting in excessive heat removal from the parison and the formation of a hard blank, which requires a large amount of surface reheating from heat retained in the core or inside of the blank in order to finally blow the parison into a finalized article.
U.S. Pat. No. 2,263,126 discloses a glass working apparatus wherein a gob of glass is intercepted during free fall by a pair of parison forming cups and deposited as a formed charge over the orifice of an orifice plate. Although the glass to metal residence time utilized during such forming may be similar to that encountered in the present invention when press forming the parison with a preshaped cavity, the actual shaping of an article from such formed charge does not materialize until after the formed charge is deposited upon an orifice plate, requiring additional residence time.
Thus, whereas the presently known press and blow processes generally form a preshaped charge of glass in a blank mold resulting in a hard blank which must be reheated before entry into the final blow mold where the parison is converted into a finished article, the present invention sets forth a method of pressing a soft blank having an initial preformed cavity, which blank passes through an elongation and development phase and then is blown into the final article.
It thus has been an object of the present invention to improve upon the known technology of delivering and forming molten glass into parisons while minimizing the amount of heat withdrawn therefrom so as to provide a soft blank which reheats well above the softness point prior to being formed into an article with relatively thin walls.